1. Field of the Invention
The field of the present invention relates to organic electroluminescent displays (OLEDs) generally, and, more particularly, to an OLED containing a desiccant formed with holes therein which prevent bubbles from forming when the desiccant is adhered to a substrate or other substantially planar surface.
2. Description of the Related Art
OLEDs offer a thinner dimension, wider viewing angle, lighter weight, smaller size, quicker response time, and lower power consumption, as compared to a cathode ray tube (CRT) display or liquid crystal display (LCD). Moreover, OLEDs can be easily fabricated using simple manufacturing processes because its simple structure includes only three major elements, namely an anode electrode, an organic material layer, and a cathode electrode. Because of these and other advantages OLEDs are emerging as the next generation of flat panel displays.
In an OLED configured in the conventional manner, an organic light emitting device is formed on a lower insulating substrate, with an upper substrate disposed above the organic light emitting device.
A significant disadvantage associated with this configuration is that materials used to form the organic light emitting layer and cathode electrode have insufficient resistance against moisture and/or oxidation. This weakness deteriorates the reliability of the display over time. In particular, internal oxidation and/or accumulation of moisture causes areas of the display to become non-emissive. Such non-emissive areas are called “dark spots”. As time goes by, the dark spots spread to neighboring areas and eventually destroy the entire display.
In an attempt to solve the foregoing problem, a conventional OLED encapsulates the organic light emitting layer and the cathode electrode to protect them against moisture and oxygen. The process involves forming a desiccant placing recess in an encapsulation substrate made of a glass material; adhering a desiccant in the recess; and bonding the encapsulation substrate to an insulating substrate with a sealant. The bonding process is performed in an inert gas such as nitrogen (N2), argon (Ar) or the like, to prevent the encapsulation of atmospheric moisture and oxygen.
Conventionally, the desiccant material is formed on a layer of adhesive material and to a thickness of about 200 μm. The desiccant material is made of barium oxide (BaO), calcium carbonate (CaCO3), calcium oxide (CaO), phosphor oxide (P2O5), Zeolite, Silicagel, Alumina, and like elements and compounds which eliminate moisture by physisorption or chemisorption.
A significant disadvantage of using the method described above is that a gas trapped between the desiccant and a substrate will form bubbles as the desiccant is adhered to the substrate. The bubbles place portions of the desiccant into contact with the organic light emitting device, which is problematic because the moisture accumulated by the desiccant eventually penetrates the organic light emitting device and makes it non-emissive.
Conventional attempts to solve the bubble problem included forming a deep desiccant placing recess to a depth of about 350 μm. This depth prevented protruding and non-protruding areas of the bubble-deformed desiccant from contacting the light-emitting device. However, because the thickness of the substrate is proportional to the depth of the desiccant placing recess, the deep desiccant placing recess necessitates a thick substrate. This, in turn, creates a heavier OLED.